JSON to TypeScript Interface Generator

Paste a JSON response and get TypeScript interfaces you can drop straight into your code. Nested objects become their own named interfaces, arrays of objects are merged so that fields missing from some items are marked optional, and values that are sometimes null become | null unions. The conversion runs in your browser, so private API data is not uploaded anywhere.

How to use this tool

1. Paste a representative JSON sample — ideally one where arrays contain several items.
2. Set the name of the top-level type (Root by default).
3. Choose interface or type alias, and whether to add export.
4. Copy the result and rename any generated type names you want to change.

Formula

string → string · number → number · true/false → boolean · null → null · [ … ] → T[] · { … } → interface

Every value is inspected and the types found at the same place are merged. A key present in only some objects of an array gets a ? (optional). Different types at one place become a union such as string | number. Identical object shapes share one interface; array item types are named from the singular of the key (orders → Order). Duplicate keys and numbers outside the supported finite, safe-integer range are rejected; other decimals use JavaScript precision.

Example

The sample user record produces three declarations. Root has id: number, name: string, tags: string[], address: Address, orders: Order[] and manager: null. Address has street, city and postcode, all strings. Order has id: string, total: number, items: number and coupon?: string — optional, because only the second order has a coupon.